Hobbing machine



Dec. 12, 1944. J. cE'rRULE HOBBING MACHINE Filed May 22,v 1942 4 Sheets-Sheet 1 l INVENTOIL (5ml/- Dec. 12, 1944. J, CE1-RULE 2,364,694

HOBBING MACHINE Filed May 22, 1942 4 Sheets-Sheet 2 SE f/ 07/ Dec. 12, 1944. J, CE1-RULE.

HoBBING MACHINE Filed May 22. m42

f1 Sheets-Sheet 3 INVENToR. io/,w ETEULE BY WM TToR/UE Dec. 12, 1944. J.' ETRULE 2,364,694,

HOBBING MACHIN Filed May 22, 1942 g 4 sheets-sheet 4 INVENTOR. JOHN C5 TR1/L E Patented Dec. 12, 19.44-

UNITED STATES TENT 4FFI'CE 2,364,694 f I I A `sionismo MACHINE John Cetrule, West Orange, N. J. v Application May 22, 1942;.ser'ia1 No. 444,135

1o claims. (creo-4) This invention relates to new and useful iniprovements in gear hobbing machines.

The invention proposes an arrangement for automatically separating theA hob from the work upon the completion of the work so that the hob feed slide may be returned to its starting position without damaging the work.

More specifically, it is proposed that a sto1 rod support the height adjustment micrometer which is mounted on the hob support slide, an that means be provided for bodily lowering said stop rod when said hob feed slide reaches its finish position. This will permit the hob feed slide to be returned to its start position Without interference between the hob and the work.

Another feature of the invention resides in the provision of a exible shaft for connecting the drive wheel of the gear hobbing machine with the hob shaft so that the hob feed slide may reciprocate while the work merely rotates. The invention contemplates constructing the flexible shaft from several rigid sections which are slidably connected and which are' also associated with flexible couplings.

Another feature of the gear hobbing machine resides in improved means for accurately set ting the hobat a slight angle to be properly aligned with the pitch of the helix of the Work being cut. It is proposed that the hob shaft be mounted in a bearing which is pivotally supported to pivot in a horizontal plane, and that means be provided for adjusting said bearing to various selected pivoted positions to accurately obtain the angle of the hob desired.

The invention also contemplates a new and novel arrangement for supporting and operating the covers for the feed change gears and the index change gears of the gear hobbing machine, whereby the covers may be easily and quickly opened and closed, singly or simultaneously, as desired.

Another feature of the gear hobbing machine resides in the provision of a steel ball to act as a thrust bearing for the work arbor in the tailstock spindle of the machine.

Still another feature of the gear hobbing machine resides in the provision of means whereby the clutch which controls the hob feed slide may be set into and out of operation so that certain resilient means be capable of urging the feed hob slide to a starting position in a preselected condition of the clutch. Specifically, it is proposed that when the clutch is opened the resilient means be capable of moving the said hob feed slide to the said starting position.

For, further cornprehensioni'l of the invention,

getti.

with

View

i is a fragmentary enlarged Vdetailed vView of aportion of Fig-3.

'Fig. 5 is a fragmentary vertical sectional lview' taken or; the une 5 5 of Fig. 2. 'l

j Fig. 6 is a fragmentary enlarged sectional View taken on the line 5 6 of Fig. 3.v i

Fig. 7. is a fragmentary enlarged sectional-view taken on the line l--l' of Fig. 3. v

Fig. V8 is a fragmentaryenlarged vertical sectionalview taken on the line 3 3 of Fig. 2 7 `Fig.9 is a fragmentary horizontal sectional view taken on the line ,S7-9 of Fig. 8.

llig..10 is a horizontal sectional View vtaken on the line lil-Hl of Fig. 8.

Fig. 11 is a fragmentary end viewloolzing in the direction of. the line Vile-fil of Fig. 9.

Fig. 12 is a fragmentary enlarged'vertical sectional gview taken on the line vl---iii of Fig. 2.

13 is a horizontalsectional view taken on thefline Iiii3 of Fig. l2. n v

Fig. :14 is a fragmentary verticalsectional view taken on the line lli-i4 lof Fig. l2.v p

Fig. 15 is a horizontal sectional view taken on `"the line 15-*45 of Fig. 14.-

Fig. 16 is a fragmentary r enlarged vertical sectional view takenuon the line iii-iii of Fig. 2. Fig 17 is a vertical sectional View taken on tnen'iine liv-l1 of Fig.l 16. A

` The gear bobbing machine;` lin accordance with this invention,y includes a housing 2Q which is mounted on a tray 2i supported on a base 22. The'housing Zil has a top recessed portion 23 across which the work arbors 2d and 25 extend. v

' The hob 26 for; operating on'the work 21 which located beneath the worlwz'a'.` The hob 2S is 4 isinounted between'the workarbors 24 and 25 is indirectly. supporteduponaLvertical hoby support slide 23 which in turn mounted ony a horizontal hob feed slidefZQ. `The-heb 26- is connected to and driven by a main drive pulley Ior Wheel 30. The pulley or whee130 is conhob support slide 28.

housing 4U to selected pivotedl positions. means includes an expansions-spring 45Llocat'ed, `to one side of the trunnion 43 and acting inJ lbeing cut on the worky 21'. y lbeen correctly set it is advisable that" the clamp nected by an endless belt 3|, or other drive, with an electric motor 32 which is mounted within `the base 22. supported on a support plate 33 which is pivot- This electric motor 32 is shown ally mounted at one end upona bracket 34. The other end of the support plate 33 is connected with a bolt 35 which is vertically slidably mounted in the top portion of the base 22 `and through.V the; traye2 lA spring 36. is coaxially mounted, onv the. bolt 35 and acts between the bottom wall of the tray 2| and the support 33 for resiliently urging the support 33 downwards so as to maintain. the tension of the belt 3|. The electric motor' 32 is provided with a three step driveA pulley., 31

which is complementary to the three steps of -the main drive pulley or wheel 3|?. Thebase 22V has a door 38 by which the interior is accessible; `At this point it may be well to state that the y `gearing hobbing machine must' be provided with `the usual liquid coolant circulating system for` icirculating the usual coolant fluid over the work Iand hob during the operation ofthe machine. However, this mechanism forms no part of 'the invention and will therefore not loe-describedV in this" specification.

The hob 26 is -xedly mountedupon a hob shaft 39 which is rotatively supported-'in a `bearing housing 40 horizontally pivotally mount- .ed by a trunnion 43 engaging apair of horizontal spaced flanges 4| and 42 on the vertical More specifically; the slide 28 has said pair of horizontal spaced flanges 4| and 42 projecting from one face between which said bearing housing 4|l-is located. Said vertical trunnion 43 is mounted centrallyon the bearing housing 40 and passes through comple-l mentary receiving openings insaid flanges 4| and 42 for accomplishing the horizontal pivotal mounting of said bearing housing. There ismeans for releasably clamping thebearing housing 40, and thus indirectly the hob shaft 39,v in selectedA pivoted positions about the trunnion 43. This means includes clamp screws 44'- mounted on the top flange-4| and abutting the top of the bearing housing 40.- When these clamp screws are loosened the bearing housing, `4t is free to pivot. Y

Means is provided for adjusting said-bearing This a horizontal direction between the rbearing housing 40 and the hob support slide 23 for tending to horizontally pivot said bearing'housing-in one direction. The bearing housing` 45 is provided `with a lug 46 which is located on the side opposite to the side having the spring 45. This lug 46 is engaged by a ne thread -screw 41,- or micrometer screw, which is mounted on a lug4'8 mounted on the hob support'slide 28. The

spring 45 functions to--pivot thev bearing housing- 40 in one direction in which the lug 46 is engaged against the end ofthe fineadjustment screw 41.v This permits the screw 41 toA be adjusted for selecting the pivoted position of the bearing housing 40;y This adjustment-makesY it `possible to set the hob 26-to a slight angle corresponding to 4the helixl anglev of the gear-teeth When the hob -26V has screws 44 be tightened Yto lock the bearing housing 40 in its position.

The hob' shaft- 39 is connected to theW main drive pulley or wheel 30 by a flexible shaft 50. This flexible shaft 50 is formed from several rigid vsections including the sections 5| and 52 which have adjacent inter-engaged'portions permitting longitudinal slidingof these sections relative to each other. The flexible shaft 50 is also provided with flexible couplings 53 interposed between sections thereof. YThe construction is such that rotations from the pulley 30 will be deliveredv to the hob shaft 3-9fin allpossible positions of said hobshaft- Itis. pointed out that the hob shaft 39 moveshorizontally, as well as vertically.

The hob shaft 39 may move horizontally becauseY it is indirectly mounted on the hob supportslide-28, which in turn is mounted on the horizontal hob feed slide 29 which moves horizontally. The hob feed slide 29 is mounted on horizontal ways 54, see Fig. 8, which are supportedon the housing 20 of the machine. The vertical hob support slide 28l is supported for vertical movement by vertical ways55, on the side of the hob feed slide 29;

The vertical position ofthe vertical hob support slide 29 iscontrolled by a micrometer 56%. This micrometer is mounted on an overheadrportion 51 of thefvertic'alfhob support slide 23y and4 rod- 58' when the hob feed slide 29 reaches-itsA finished position. Thismeans includes a shaftv59 rotatively mounted on the hebv feed slide- 23 andA turned by certain mechanism. This shaft55f carries aV cam- 66 which engages a bottom section 6| of the-stop rodv 58'- Inone position o1- theshaft 59 the stop rod 58-is7held ina raised posi#V tion, and in a turned position-of the shaft 59' thestop rodf58-'willbe in its lowered position. In the lowered position of the stop vrod-5|llthe 'vertical hob support slide 281 will lie-in-v aA down -position and the; hobv 26. will be free from the-work 21 sothat the hob feed slide 291may move toits starting position, andthe hob-v will not: collide and damage the finished work21. v

The stopvrod 58 isvformed4 fromtwosections;

namely., the bottom section-5f! and a tubular top` I section 62v which is 'rotatiively-supported ori-a flangev 1040i the hob feed slide 29e;l The imi'c-:rometer 55 engages thistop section 62: The top'isectijon4 62 is provided with a-flange portionf having gear teethl 53 whichr mesh with the teeth of a longverticalgear 64. This gear 64 is vmounted on-` a spindlei65 Vhaving a head faccessiblef'or manual turning. The bottomsection 6| ofthe-stoppin- 58 is provided with akey tlengaging acomplementary slot in a flange 68 on tl`iehobfeedL slide 29'. The sections 61|gand 52 aretl'ireadedly connected with each other bythe threads-- 69.-

The construction is suchr that :thelheadvtmayhbe manually turned for indirectlyA turning thesection 62? of the stop rod' 58and causing itto be moved' upwards or downwards to a selected position. With thisY construction it-is possible-toI set the stop roel` 58fto selected conditions- The micrometer 56 is used for-line adjustments.-

The main drivey pulleyvorwhcel 33E-'is mounted on -a shaft 13 which is rotatively-'supported' on` aflange 1| of thehousing-26li Back of'fthisla'nge' 1| there areindexingchange-gears12i- More specifically, thepulley 3|) whic'li-A isan'ounted on-4 The main feed slide shaft 94.

said shaft 13 connects with a. gear 14 on said shaft 13. This gear V'i4 meshes with agear 15 xed to another gear 16. Thegears 15 and 16 are rotatively supported upon an arm 11 which is pivotally mounted on said shaft 13. has a flange 19 engaged by a washer 89 .which may be clamped down tightly by a cap screw 8| mounted on the flange 1|.V The construction is such that the cap screw 8| may be loosened and then the arm 11 is free to swing. A gear 32 is mounted on the .shaftlf and meshes with the` gear 19. The construction is such that the gears 15 and 13 may be removed and replaced by other gears and these new gears may be properly meshed with the gears 1li` and 82 by setting the arm 11 in a proper position.

The shaft 18 is rotatively supported in the housing 2G and extends from the back of the machine to the front of themachine and is provided with a spiral pinion 83 meshing with a spiral gear 84 on the head stock spindle 95 which supports the work arbor 24. AThe head stock spindle 85 is provided with another spiral gear 80 meshing witha spiral gear 81 on a rotatively supported shaft 39 which extends to the front of a `flange 1| of the housing 20. The shaft 88 is provided with a gear 89 meshing with a gear 99 on a rearwardly extending shaft 9|. The gears 89 and 99 are removable and changeable with other gears,` and comprise feed change vgears of the gear hobbingmachine. The shaft 9| extends rearwards and is providedwith a spiral gear 92 meshing with a spiral gear 93 mounted on the This shaft 94 is rotatively supported in the housing 20 and is indirectly connected to drive the hob feed slide 29.

More specifically, the main' shaft 94 is connected with a rotatively supported auxiliary shaft 95 by a friction clutch 99. The friction clutch 96 has a section 91 mounted on the shaft 94, and a complementary section 9S Ymounted on the shaft 95. A spring 99 acts between a flange |90 on rthe shaft 95 and a'station'aryv-bracket |01, and normally tends to urge the clutch 99 open. The clutch 93- is held closed by a screw |02. This screw |02 is threadedly mounted through `a wall of the housing It is provided with a hand wheel |33 by .which it Ymay be operated. The screw |92 is rfreely rotatively connected by a thrust bearing |94 with the adjacent end of the shaft 95. The construction is such that the hand wheel |03 may be turned in one direction for closing the clutch 93,- land then rotations will be transmitted from the shaft 94 to the shaft 95. The hand wheel |93 may be turned in the other direction for turning the screw |02 outwards a smallamount so that the spring 99 may open the clutch 96..

A spur gear |05 is mounted on the shaft 95 and meshes with a gear |06 mounted on the feed screw |01 of the hob feed slide 29. This screw |01 is rotatively supported and threadedly connects with a follower |08 which is connected with the feed slide 29. The feed slide 29 is provided with a flange |09 from which several rods ||0 extend inwards through openings in a wall of the housing 20. `Expansion springs are mounted on the rods ||0 and act vagainst the housing 20 and flange |09 and normally urge the hob feed slide 29 to its starting position. When the clutch 95 is closed the shaft 94 is capable of turning the screw |01 and driving the hob feed slide 29 to its nished position.' However, when the hand wheel |03 is manipulated to open the clutch 9B thesprings |||are then, .and only The arm 11 then, capable of forcing the hob-feedslide 29 back t0 its starting position. During'thisoperation the screw |01, which is a steep thread screw, merely turns. g l n The head stock spindle is provided with` a collet clutch ||2 which supports the Work arbor 2 4,v The work arbor-25 is indirectlysupported upon a tailstock spindle I3. This tailstockspindle I3 supports a bushing I4 which in turnlsupports the work' arbor 25. A cap ||5 is threadedly and removably mounted on the bushing 4. A rod ||6 passes through the tailstock spindle 3 and has a reduced front end ||1 which `threadedly engages the inner end of the bush;- ing 114. A steel Yball ||8 is located within the bushing V| I4 and` engages, against vtheadjacent end.. of the rod I6 and forms la thrust bearing for the work arbor 25.y The outer end of the rod ||6 is threadedand a nut I|9 is threadedly mountedon this latter end and engages the end of the tailstock, spind1e,||3.

A handlel |20 radially projects from the tailstock spindle ||3 and passes through a bayonet slot 2 i in a tube |22 whichis adjustably` mounted on a supportl portion |23 of the housing20. A `set screw |24 holds the tube |221in adjusted positions. The baypnet slot |2| has a Ilongitudinally extending,V portion ,|25 and a transversely extending portion126. When the handlefv |20 Vis' in the transverse portion |25 the work arbor 25 will be in its operative position. The handle |20 may be moved` to the free end of the longitudinal section |25 of the bayonet slot |2|, and

then the tailstock` spindle 3 will be retracted 4v3:5

and the work arbor 25 similarly moved.

The means for bodily lowering the stop rod 58 previously referred to when the hob feed slide` 29 reaches its finished position, vincludesa handle |21 fixedly mounted on an extended end of the shaft 59. 4.A catch |28 is also mounted on the shaft 59 and engages a complementary catch |29 pivotallymounted on a pintle |30 supported on' the hob feed slide |29. The catch |29 has a tail |3| which is in line with a rod |82 adjustably mounted by a stationary clamp |33 mounted on the housing 29. A rod |34 pivotally connectswith the handle |21 and extends downwards and pivotally connects with the operator lever |35 of aswitch |36 which is connected to control the operation of the motor 32. The electrical connections of switch and motor will not be given in this specification* as it forms no part of the invention, and such connegtions would beknown to those skilled inthe ar -The rod 34 is made of twosections adjustably connected by a coupler |31. The clamp |33 may be opened and the rod |32 adjusted'to a selected position which will control the 'nished position of the hob feed slide 29. hob feed slide reaches its finished position the tail |3| of the hook |29 will strike the rod |32.

This will pivot the hook`|29 free from the hook |28. This releases the shaft 59 and thehandle |21 will fall downwards, pivoting the shaft 59.v

|36, stopping the electric motor 32.k

The vstarting position' of the hob feed slide 29 is controlled by a stationary stop |38 which is flxedly mounted on the hob feed slide |29 by a screw- |39. A rod |40 is adjustably supported kby a .clamp |4| stationarily mounted on the housing` 20. The construction is suchthat'the when the` 'heb freed slide 29 Shay 'twaresahegrcd 11m fantil Itriefstep l 3s :trie-'rea Mus' The index change gears12 are ldatediipn y assente@ |49f1of theparticular'arm l(arm |45 orf-arm |48) of the .particular covers 'upwards `to, its raised position'and -then trnjsaid pin |49 90 so 'that the ke'y- |50 Ythereof rnow rests on said arm, holding the pin |49 raised. Now the handle |6| may beft'urn'e'd for again driving the'slide |56 towards opened. This "cover may '-be -Ireclosed fand the pin |49 which -is raised, moved back to its lowered `fpos'ition, and the deviceisA -now back inits' original condition.

'The operation of -the gear -lhobbing machine is as follows: 1

iii() -|f46--is provided withfop'enings W62, 'e'ach extend'- lreleases-1y homing Ythe `covers :in their fc'idsed position. v

closed positions. -Iffitfisdesiredtofopen b't 'ne Rotations -from themotor -32 vwill `drive the pulley 30,-which-in turn will drivethe holo shaft 39 driving the hob l2li. Simultaneously, -rotations from "the pulley #30., through the index change gears 'I2 and the spiral gears 83 and'84 will driverthe headstockspin'dlef=l85. The head stock fspindle -65 drives the work arbors'24 and 25` Simultaneously, while this is happening, -rotations of Athe head stock-spindle 85 through the ggearsi fand "81 and 4the `feed change gearsf89 and 90, will indirectly drive thehob :feed .slide main shaft 94. Therotations fromv-saidvshaft '94 wi1l-be L'transmitted by the friction clutch 9G to indirectly drive the hoblfeed vslide 29. The hob -26 -is now cutting the work-21. When the hob feed 'slide M29 reaches itsfinished position the wrk-2'| Vwill-be finished. `In the flnishedrposition-of the hob feed slide 29, the tail |3| of the hook |29 will' engage -thel rod' |32 Ywhich indirect` ly'will cause turning of 'i the shaft v59 which will drop the vertical hob feed slide v28. At the same time turning lof theshaft59 will indirectl'yoperatethe-switoh |36, cutting-01T the Vmotor 32. The machine has now finished its work.

The hand -W-heel |03 lmay now be turned to open ythe clutch -`96. The springs will immediately return thehobfeed slide 29 Atoits starting position. The handle |20 may bemanipulated to .release the work 21. Newwork is now placed betweenthearbors24 and 25. The handle |21 isv now turned back to its .original posi- -tion which turns the-shaft 59, which raises `the stoprod `53 which-indireetlymoves the hobsup- .port'slide 28 back Ai'vowits-'raise'd position. When the vrhandle |2Twas raisedfthes'witch |36was indirectly closed, re-starting the motor 32 and the machine is now starting its "operation on the new work.

While I haveillustr-ated and described. the preferred embodiments o f myfinvention, it is to be understood"that I do not limit myself to the precise constructions herein disclosedand the right isi re'servedto all changes and niodifioationscoming Within ftheffscope ef-the invention was dened inithe appended vclaims.

flflaving 1thus i described frny invention, what Y 'I cla-im asrnew and-'desiife-to2secure by V'United statesinetters Patentis:

51. l'-In f a gear h'bbing lmachine, 'ia horizontal `holo feed slide, -m'eans flor I said :Thob 'feed slide to a'nishl positinxla -'vertical"h'ob "support asi-idewmountedlonrsaidhobffeedsslida'astopfrod tvertically 'slidably @mounted "Ton said `h'olo lfe'e'd slide," a ahei'g'htffadiustnient .micrometer mounted onsai'd hobr 'siipp'rtslide1arrd1resting 'on' isaidr stop rod, and means-'riorbo'dily :loweringfsaid stoprod when saidihob feedfslide i'ealiesfits'nish p'osition.

hob feed slide, means for driving said hob feed slide to a finish position, a vertical hob support slide mounted on said hob feed slide, a stop rod vertically slidably mounted on said hob feed slidefa height adjustment micrometer mounted on said hob support slide andresting on said stop rod, and ,means for bodily lowering said stop rod when said hob feed slide reaches its finish position, said stop rod having a top end portion vertically adjustably mounted on a bot- `tom portion, -and said micrometer being supported by said top end portion.

3. In a gear hobbing machine, a horizontal hob feed slide, means for driving said hob feed slide to a finish position, a vertical hob support slide mounted on said hob feed slide, a stop rod vertically slidably mounted on said hob feed slide, a height adjustment micrometer mounted on said hob support slide and resting on said stop rod, and means for bodily lowering said stop rod when said hob feed slide reaches its finish position, said stop rod having a top end portion vertically adjustably mounted on a bottom portion, and said micrometer being supported by said top end portion, said top end portion being threadedly mounted on said bottom portion, and

means for rotating said top end portion relative to the bottom portion for attaining said vertical adjustment.

4. In a gear hobbing machine, a horizontal hob feed slide, means for driving said hob feed slide to a finish position, a vertical hob support slide mounted on said hob feed slide, a stop rod vertically slidably mounted on said hob feed slide, a height adjustment micrometer mounted on said hob support slide and resting on said stop rod, and means for bodily lowering said stop rod when said hob feed slide reaches its finish position, said stop rod having atop end portion vertically adjustably mounted on a bottom portion, and said micrometer being supported by said top end portion, said top end portion being threadedly mounted on said bottom portion, and means for rotating said top end portion relative to the bottom portion for attaining said vertical adjustment, said last named means comprising a gear portion on said top end portion, another gear meshing with said gear portion and adapted to be manually turned.

5. In a gear hobbing machine, a vhorizontal hob feed slide, a vertical hob support slide mounted on said hob feed slide, a hob shaft rotatively mounted on said hob support slide, a rotative drive pulley located backwards of said hob shaft, said hob shaft being mounted in a bearing, said bearing being pivotally supported to pivot in a horizontal plane, means for releasably clamping said bearing in selected pivoted positions, and means for adjusting said bearing to selected positions, comprising resilient means tending to pivot said bearing in one direction, and an adjustment screw for holding said bearing in various selected positions against the action of said spring.

6. In a gear hobbing machine, a horizontal hob feed slide, a vertical hob support slide mounted on said hob feed slide, a'hob shaft ro" a lug projecting from the bearing, an adjust-` ment screw engaging against said lug for moving the bearing to various positions, and resilient means tending to pivot said bearingto hold its lugs engaged against said adjustment screw.

7. In a gear hobbing machine, a pair of opposed woik arbors for vholding work between them, a driven heads'tockl spindle supporting one of said arbors, a tailstock spindle for the other arbor, ar bushing surrounding said last mentioned arbor and extending into said tailstock, a rod mounted through said tailstock spindle and connected with said bushing, and a steel ball within said bushing and engaging against an adjacent end of said rod and arbor.

8. In a gear hobbing machine, a horizontal hob feed slide, a steep angle hob feed screw beneath said slide, a follower from said slide engaging said screw, resilient means urging said hob feed slide to a starting position, a hobyfeed drive shaft, a transmission from said drive shaft to said screw and including a clutch, and means for opening said clutch, whereby said resilient means returns said hob feed slide to its starting position.

9. In a gear hobbing machine, a horizontal hob feed slidea steep angle hob feed screw beneath said slide, a follower from said slide engaging said screw, resilient means urging said hob feed slide to a starting position, a hob feed drive shaft, a transmission from said drive shaft to said screw and including a clutch, and means for opening said clutch, whereby said resilient means returns said hob feed slide to its starting position, comprising resilient means tending to open said clutch, and a screw opposed to said resilient means for holding said clutch closed.

10. In a gear hobbing machine, a horizontal hob feed slide, a steep angle hob feed screw beneathl said slide, a follower from said slide engaging said screw, resilient means urging said hob feed slide to a starting position, a hob feed drive shaft, a transmission from said drive shaft to said screw and including a clutch,.and means for opening said clutch, whereby said resilient means returns saidvhob feed slide to its starting position, said resilient means comprising expansion springs acting ,between said hob feed slide and a stationary part of said gear hobbing machine.

JOHN CETRLE. 

